This is why European patent EP-0.633.008 submitted by the applicant proposes to use compressed carbon dioxide (CO.sub.2) as a source of cooling for cryotherapy, the intrinsic characteristic of carbon dioxide being that it can reduce the temperature down to -78.degree. C. at atmospheric pressure. According to the information provided in this patent, the use of carbon dioxide in the form of a liquid/vapor mix can keep the pressure in the receptacle constant while it is being emptied; this pressure is simply the saturating vapor pressure which depends directly on the temperature of the receptacle. Thus, carbon dioxide occurs in two phases (namely solid and gas) when the pressure is reduced to atmospheric pressure. The solid phase, also called dry ice, extracts the maximum amount of heat from the skin of the patient to be treated. When it comes into contact with the skin, dry ice sublimates and thus absorbs a large quantity of heat. It is therefore essential to extract carbon dioxide from the receptacle in the liquid phase in order to produce intense cold and an extremely fast temperature drop at the same time.
In order to achieve this result, the apparatus according to the previous patent includes a plunger tube inside a pressurized liquid carbon dioxide cylinder, this plunger tube starting from the top of the cylinder and extending over its entire length. Thus, the liquid phase of CO.sub.2 is drawn off and is then sprayed into a flexible pipe by means of a pressure reduction and ejection system fitted with a control handle and a diffuser which adjusts the shape, dimension and temperature of the CO.sub.2 jet on the area to be treated.
This apparatus is heavy, and is used mainly by professionals such as physiotherapists. It is completely unsuitable for any environment other than conventional traumatology departments, for example such as sport grounds, racing courses or stud farms.